3e SRD:Armor for Unusual Creatures

From D&D Wiki

The information on Table: Armor is for Medium-size creatures. Armor for Tiny or smaller creatures costs half as much as that for Medium-size creatures, provides half as much protection, and weighs one-tenth or less as much. Armor for Large characters costs double and weighs twice as much, and for Huge creatures it costs quadruple and weighs five times as much. Armor for even larger creatures must be specially made and has no standard price or weight.

Armor for a nonhumanoid creature costs twice as much as the same armor for a humanoid.